Aqueous polymerization, including solution and emulsion polymerization, generally may be carried out successfully, if in the case of a solution polymerization the starting monomers and resulting polymer are water soluble and in the case of an emulsion polymerization the starting monomers not having very low water solubility. However, a number of problems are encountered if the aqueous polymerization is:
(a) a solution polymerization of at least one monomer having low water solubility; or PA1 (b) an emulsion polymerization of at least one monomer having very low water solubility. PA1 (1) poor conversion of the monomer having low water solubility evidenced by monomer pooling around the stirrer shaft and the presence of monomer droplets in the final product; PA1 (2) high gel or coagulum levels; PA1 (3) the formation of emulsion or suspension polymer during a solution polymerization or large suspension polymer particles during an emulsion polymerization; PA1 (4) phase separation or creaming of monomer droplets or large suspension particles; and PA1 (5) abnormal (non-kinetic) distribution of the monomers having high water solubility and the monomers having low water solubility because of the nonuniform distribution during polymerization of the two types of monomers evidenced by multiple glass transition temperatures as measured by differential scanning calorimetry. PA1 (a) from a monomer having low water solubility with either: PA1 (b) resulting in a polymer, while formed from monomers having high water solubility, which has low water solubility PA1 (a) the addition of at least about 5-30% by weight, based on total monomer weight, of an organic solvent; PA1 (b) the use of a comonomer which acts as a solvent for the monomer having low water solubility; or PA1 (c) the use of a high level of surfactant. PA1 (1) complexing at least one monomer having low water solubility with a macromolecular organic compound having a hydrophobic cavity; and PA1 (2) polymerizing in an aqueous system from about 0.1% to about 100%, by weight of the monomer component, based on the total weight of the polymer, of the complexed monomer having low water solubility with from about 0% to about 99.9% by weight, based on the total weight of the polymer, of at least one monomer having high water solubility.
Problems are also encountered if an aqueous solution polymerization produces a final polymer having low water solubility.
These problems include:
Attempts to overcome these problems when forming polymers, particularly in a random arrangement:
(i) another monomer having low water solubility; or PA2 (ii) a monomer having high water solubility in an aqueous system either by aqueous solution or emulsion polymerization; or
has not heretofore been satisfactory without at least one of the following to aid in solubilizing the monomer or final polymer having low water solubility:
For example, U.S. Pat. No. 4,268,641 describes the synthesis of copolymers of acrylic acid with hydrophobic nonionic surfactant acrylates via solution polymerization requiring organic solvents including aromatic, saturated aliphatic, cycloaliphatic and halogenated solvents to facilitate the reaction. For example, U.S. Pat. No. 4,734,205 describes the synthesis of copolymers of acrylamide, acrylic acid or its salts with hydrophobic alkylacrylamide or alkyl (meth)acrylate requiring high levels of surfactants to effect polymerization.
The addition of an organic solvent or high level of surfactant poses safety, health and environmental problems. The addition of a solvent may also destabilize aqueous systems to which it is added.
I have discovered a method for forming in an aqueous system a polymer containing, as polymerized units, at least one monomer having low water solubility by solution or emulsion polymerization without the addition of an organic solvent or high level of surfactant surfactant to aid in solubilizing the monomer or final polymer having low water solubility and, thus, without the attendant safety, health, environmental and stability problems associated with organic solvents and high levels of surfactants.